Abstract The human amy ygdala is a c in structure made up of a number of nuclei, which together are vital for complex brai an array of emo 18-23 otional and s viors that con evelop across adolescence. While a number social behav ntinue to de of structural MR ave examined sex differe mygdala maturation, these studies have reported RI studies ha ences in am mixed findings.12-17 Moreove tudies sugge cific and heterogeneous effects of testosterone er, animal st est sex-spec on the developm of var subnuclei within the amygdala.8-10 However, confirming similar patterns o ment rious r of growth in humans has been n limited by the inability ly segment amygdala subnuclei in adolescents y to precisel using MRI. Using a large NIH-funded im etic, and hormone adolescent dataset (N=450; ages 10-18 maging, gen yrs.; PI: Nagel), the current proposal aim ms to adapt a new in vivo amygdala segmentation approach to assess structural segme entation of amygdala s cross adolescence. Following individually based subnuclei subnuclei ac delineation, we a determine ho rone levels and androgen receptor (AR) sensitivity relates to also aim to d ow testoster neurotypic amy subn volum in adolescent oys and girls. Elucidating struc sexua ygdala nuclei mes bo g tural al dimorphisms in amygdala s humans ma ur understanding of amygdala development, as subnuclei in ay aid in ou well as ultimately help us to understan sex differences in various behaviors and risk for disease.7 nd life-long s Moreover, this r research wil ly contribute ger field of developmental neuroscience, as the ll significantl e to the larg current study ai date a meth process by which we can segment amygdala subnuclei in ims to elucid hodological p developing samp methods sh eful to a wide array of researchers who may wish to create ples. These hould be use specific normativ inical pediatr s for future structural, functional, and diffusion MRI studies. ve and/or cli ric templates